NEW ISOLATION METHODS AND POLYMERASE CHAIN-REACTION STRAIN DISCRIMINATION TECHNIQUES FOR NATURAL-PRODUCTS SCREENING PROGRAMS

A new isolation method of fungi was established by using the Percoll d ensity gradient centrifugation. We found that the difference in the sp ecific gravity allowed us to separate mixtures of fungal spores of Asp ergillus, Fusarium, Listeromyces, Penicillium, and Trichoderma. When t his technique was applied to soil samples, a wider variety of fungi we re isolated compared with those obtained from an ordinary serial dilut ion method. For screening purposes, it is necessary to eliminate redun dant strains from the strains initially isolated. For the efficient di scrimination of strains, the random amplified polymorphic DNA (RAPD) m ethod was applied. The establishment of a standard method for RAPD ena bled us to minimize the deviation of R(f) values between gels to less than 0.03. Conversion of the R(f) values to binary matrices provided a matrix data that could be analyzed statistically. Based on the RAPD, it was possible to select genetically distinct fungal strains within a species.